In many industries, such as automotive manufacturing, components are formed using a transfer press. At a basic level, a transfer press comprises a press bed supporting one or more lower dies; a slide carrying one or more upper dies corresponding to the lower dies; and a crown for raising and lowering the slide relative to the press bed. Components are formed by positioning materials between the upper and lower dies and lowering the slide to press the material between the upper and lower dies, thus modifying the material between the dies according to the configuration of the dies. After the initial press, the component is transferred to an adjacent set of dies, and the process is repeated to further modify the component. This process is repeated at until the component has been modified as desired.
Transfer presses are typically large, often over fifty feet tall. To accommodate these machines within reasonably sized manufacturing facilities, the transfer presses are generally assembled and operated in a pit extending below the floor level of the facility. Manufacturers of these presses often assemble the presses within similar pits at their own facilities to allow customers to view the press before purchasing it. The total time necessary to assemble the press is determined, in large measure, by the `pit time,` corresponding to the assembly occurring within the pit. Assembling components within the pit generally takes much longer than assembling at floor level because only one level of components may be assembled at a time.
Often, it is desirable to use a single elongated bolster to carry the plurality of lower dies associated with the work stations within the press. These bolsters are generally supported by wheels at either end, which facilitate moving the bolster in and out of the press frame to exchange sets of dies. Each set of wheels is typically driven by one or more drive mechanisms. A problem with this approach is that the single elongated bolster is often too heavy to assemble outside of the pit in which the press operates. Assembly thus requires considerable pit time, which greatly increases the total assembly time of the press. Another problem with this approach is that the large bolsters are often difficult and expensive to transport.
Still another problem with this approach is that the wheels supporting the bolster are often placed at either end of the elongated structure. This allows excess deflection of the bolster during operation of the press. In addition, because the wheels supporting the bolster typically reside at either end, long drive mechanisms, or multiple drive mechanisms are typically used to drive the wheels to move the bolster. This results in extra weight and expense.